As a fuel cell, a Solid Oxide Fuel Cell (to be also referred to as SOFC), in which a solid electrolyte (solid oxide) is used, is conventionally known.
Used as the SOFC is a stack wherein, for the purpose of increasing electrical power, a number of fuel cells, having a fuel electrode and an air electrode on each surface of a solid electrolyte formed in, for example, a plate shape, are stack-layered through a separator (for example, interconnector). The SOFC generates electricity by supplying fuel gas (for example, H2, methane, ethanol, and so on) to the fuel electrodes, supplying oxidant gas (for example, air) to the air electrodes, and causing a chemical reaction via the solid electrolyte between the fuel and oxygen contained in the air.
In the above mentioned SOFC stack, a vent for gas introduction is formed inside the SOFC in order to supply fuel gas and oxidant gas to the cell of each layer (so-called internal manifold structure). Gas is supplied to each cell via a flow path of each separator from the vent.
Also, in this type of SOFC stack, each cell is electrically connected in a stack-layering direction. Hence, in order to increase electrical power of the whole stack, it is important how homogeneously and efficiently each cell is operated.
However, when electricity generation is actually performed by the SOFC stack, it is not easy to homogeneously and efficiently operate the cell in each layer. The known reasons for this are because: (a) gas is not uniformly distributed to the cell of each layer, and (b) difference occurs in operating temperature between the end part and the center part of the stack.
As the measures against the above (a), a manifold structure is proposed which enables uniform supply of gas (see Patent Document 1).
Also provided as the measures against the above (b) are an external manifold system which transfers heat in the center part to the end part (see Patent Document 2), and a structure including pipes that are connected to respective layers inside a manifold (see Patent Document 3).    Patent Document 1: Unexamined Japanese Patent Publication No. 2004-207008    Patent Document 2: Unexamined Japanese Patent Publication No. 2004-022343    Patent Document 3: Unexamined Japanese Patent Publication No. 2005-203255